Photodetector device comprising each of a plurality of passive quenching elements connected in series to at least one avalanche photodiode and a capacitative element connected in parallel to the passive quenching element

ABSTRACT

A photodetector device includes an avalanche photodiode array substrate formed from compound semiconductor. A plurality of avalanche photodiodes arranged to operate in a Geiger mode are two-dimensionally arranged on the avalanche photodiode array substrate. A circuit substrate includes a plurality of output units which are connected to each other in parallel to form at least one channel. Each of the output units includes a passive quenching element and a capacitative element. The passive quenching element is connected in series to at least one of the plurality of avalanche photodiodes. The capacitative element is connected in series to at least one of the avalanche photodiodes and is connected in parallel to the passive quenching element.

TECHNICAL FIELD

The present invention relates to a photodetector device.

BACKGROUND ART

A photodetector device in which a plurality of avalanche photodiodes aretwo-dimensionally arranged is known (for example, Patent Literature 1).The plurality of avalanche photodiodes is arranged to operate in aGeiger mode. The plurality of avalanche photodiodes are formed on asemiconductor substrate formed from compound semiconductor.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Unexamined Patent Publication No.    2012-531753

SUMMARY OF INVENTION Technical Problem

In a case where a plurality of avalanche photodiodes formed on thesemiconductor substrate formed from the compound semiconductor isarranged to operate in the Geiger mode, a dark pulse and an after pulseincrease in correspondence with a temperature variation. When a noiseincreases due to the dark pulse and the after pulse, there is a concernthat a signal from the avalanche photodiodes may not be appropriatelydetected.

There is known a configuration in which passive quenching elements arearranged in series to the avalanche photodiodes to quench avalanchemultiplication in a case where the avalanche photodiodes is arranged tooperate in the Geiger mode. Whether or not an avalanche multiplicationprocess that occurs inside the avalanche photodiodes connected to thepassive quenching element is appropriately quenched is determineddepending on a resistance value of the passive quenching element. Whenthe resistance value of the quenching elements is not sufficient, thereis a concern that appropriate quenching is not realized due tooccurrence of a latching current or the like. It is necessary to selecta sufficient resistance value of the quenching elements for appropriatequenching.

As the resistance value of the passive quenching elements is larger,time necessary for quenching of the avalanche photodiodes which areconnected to the passive quenching elements in series increases. As thetime necessary for the quenching increases, dead time for which lightcannot be detected by the avalanche photodiodes increases. As describedabove, there is a demand for a circuit design including passivequenching elements having an optimal resistance value to makeappropriate quenching and reduction of the dead time compatible witheach other and to secure photodetection sensitivity and photodetectiontime resolution.

Since a parasitic capacitance in the passive quenching elements also hasan influence on a pulse signal, and thus removal of the parasiticcapacitance is also demanded. It is also demanded to improve a peakvalue of the pulse signal to further improve the photodetection timeresolution. It is very difficult to design a device in which theplurality of avalanche photodiodes formed on the semiconductor substrateformed from the compound semiconductor are arranged to operate in theGeiger mode so as to satisfy all of the above-described desiredconditions.

An object of an aspect of the invention is to provide a photodetectordevice in which photodetection sensitivity and an improvement ofphotodetection time resolution are compatible in a configuration inwhich a plurality of avalanche photodiodes are formed on a semiconductorsubstrate formed from compound semiconductor.

Solution to Problem

According to an aspect of the invention, there is provided aphotodetector device including an avalanche photodiode array substrateand a circuit substrate. The avalanche photodiode array substrate isformed from compound semiconductor. The avalanche photodiode arraysubstrate is mounted on the circuit substrate. A plurality of avalanchephotodiodes are two-dimensionally arranged in the avalanche photodiodearray substrate. The plurality of avalanche photodiode is arranged tooperate in a Geiger mode. The circuit substrate includes a plurality ofoutput units connected to each other in parallel. The plurality ofoutput units form at least one channel. Each of the output unitsincludes a passive quenching element and a capacitative element. Thepassive quenching element is connected in series to at least one of theplurality of avalanche photodiodes. The capacitative element isconnected in series to at least one of the avalanche photodiodes, and isconnected in parallel to the passive quenching element.

In this aspect, the plurality of output units including the passivequenching element and the capacitative element are provided in thecircuit substrate different from the avalanche photodiode arraysubstrate. According to this, a space capable of forming the pluralityof output units can be further expanded in comparison to a case wherethe plurality of output units are arranged in the avalanche photodiodearray substrate. When the output units are provided in the circuitsubstrate separate from the avalanche photodiode array substrate, aparasitic capacitance that occurs between a configuration of theavalanche photodiodes and the output units can be reduced. In this case,a manufacturing process different from that of the avalanche diode arraysubstrate can also be used. Accordingly, the design of the plurality ofoutput units becomes easy. The capacitative element provided in thephotodetector device is connected in series to at least one of theavalanche photodiodes and is connected in parallel to the passivequenching element. According to this, a peak value of a pulse signaltransmitted from the avalanche photodiode that is connected in series tothe capacitative element can be improved due to the electrostaticcapacitance of the capacitative element. Accordingly, a pulse signaltransmitted from the plurality of avalanche photodiodes is easilydetected, and light detection resolution can be further improved.

In the aspect, the passive quenching element may be formed by a firstpolysilicon layer provided in the circuit substrate. The capacitativeelement may be formed by a second polysilicon layer provided in thecircuit substrate, a dielectric layer stacked on the second polysiliconlayer, and a third polysilicon layer stacked on the dielectric layer.The first polysilicon layer may be formed at the same height as in thesecond polysilicon layer or the third polysilicon layer in a thicknessdirection of the circuit substrate. In this case, the plurality ofoutput units can be formed by a simple manufacturing process.

Advantageous Effects of Invention

According to the aspect of the invention, there is provided aphotodetector device capable of securing photodetection accuracy with asimple design in a configuration in which a plurality of avalanchephotodiodes are formed on a semiconductor substrate formed from compoundsemiconductor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a photodetector device according to anembodiment.

FIG. 2 is a view illustrating a cross-sectional configuration of thephotodetector device.

FIG. 3 is a plan view of a circuit substrate.

FIG. 4 is a plan view of a photodetection region of an avalanchephotodiode array substrate.

FIG. 5 is a view illustrating a configuration of a circuit substrate.

FIG. 6 is a view illustrating a circuit configuration capable of beingused in the photodetector device.

FIG. 7 is a view illustrating a circuit configuration capable of beingused in a photodetector device according to a modification example ofthis embodiment.

FIG. 8 is a plan view of a mounting region of the circuit substrate.

FIG. 9 is a view illustrating components of a pulse signal transmittedfrom an avalanche photodiode.

FIG. 10 is a view illustrating characteristics of a recharge pulse.

FIG. 11 is a view illustrating characteristics of a fast pulse.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the invention will be described in detailwith reference to the accompanying drawings. Note that, in description,the same reference numeral will be given to the same elements orelements having the same function, and redundant description thereofwill be omitted.

First, a whole configuration of a photodetector device according to thisembodiment will be described with reference to FIG. 1 to FIG. 8. FIG. 1is a perspective view of the photodetector device according to thisembodiment. FIG. 2 is a view illustrating a cross-sectionalconfiguration of the photodetector device according to this embodiment.In FIG. 2, hatching is omitted to improve visibility. FIG. 3 a plan viewof a circuit substrate. FIG. 4 is a plan view illustrating a part of anavalanche photodiode array substrate. FIG. 6 is a view illustrating acircuit configuration capable of being used in the photodetector deviceaccording to this embodiment. FIG. 8 is a plan view illustrating a partof the circuit substrate.

As illustrated in FIG. 1, a photodetector device 1 includes an avalanchephotodiode array substrate 10 and a circuit substrate 50. Hereinafter,“avalanche photodiode” is referred to as “APD”. “Avalanche photodiodearray substrate” is referred to as “APD array substrate”. The circuitsubstrate 50 is disposed to face the APD array substrate 10. The APDarray substrate 10 and the circuit substrate 50 have a rectangular shapein plan view.

The APD array substrate 10 includes a main surface 10A and a mainsurface 10B which are opposite to each other, and a side surface 10C.The circuit substrate 50 includes a main surface 50A and a main surface50B which are opposite to each other, and a side surface 50C. The mainsurface 10B of the APD array substrate 10 faces the main surface 50A ofthe circuit substrate 50. A plan parallel to the respective mainsurfaces of the APD array substrate 10 and the circuit substrate 50 isan XY-axis plan, and a direction orthogonal to the respective mainsurface is a Z-axis direction.

The side surface 50C of the circuit substrate 50 is located on an outerside in the XY-axis plane direction in comparison to the side surface10C of the APD array substrate 10. That is, in plan view, an area of thecircuit substrate 50 is greater than an area of the APD array substrate10. The side surface 10C of the APD array substrate 10 and the sidesurface 50C of the circuit substrate 50 may be flush with each other. Inthis case, in plan view, an outer edge of the APD array substrate 10 andan outer edge of the circuit substrate 50 match each other.

A glass substrate may be disposed on the main surface 10A of the APDarray substrate 10. The glass substrate and the APD array substrate 10are optically connected to each other by an optical adhesive. The glasssubstrate may be directly formed on the APD array substrate 10. The sidesurface 10C of the APD array substrate 10 and a side surface of theglass substrate may be flush with each other. In this case, in planview, the outer edge of the APD array substrate 10 and the outer edge ofthe glass substrate match each other. In addition, the side surface 10Cof the APD array substrate 10, the side surface 50C of the circuitsubstrate 50, and the side surface of the glass substrate may be flushwith each other. In this case, in plan view, the outer edge of the APDarray substrate 10, the outer edge of the circuit substrate 50, and theouter edge of the glass substrate match each other.

The APD array substrate 10 is mounted on the circuit substrate 50. Asillustrated in FIG. 2, the APD array substrate 10 and the circuitsubstrate 50 are connected to each other by the bump electrode 25.Specifically, as illustrated in FIG. 3, the APD array substrate 10 isconnected to the bump electrode 25 over a mounting region α disposed atthe center of the circuit substrate 50 when viewed from a thicknessdirection of the APD array substrate 10. In this embodiment, themounting region α has a rectangular shape.

The circuit substrate 50 includes a ground line 3, a cathode line 5, andan anode line 7 at the periphery of the mounting region α. The groundline 3, the cathode line 5, and the anode line 7 extend from themounting region α. The ground line 3 is connected to a ground electrode63 to be described later. The cathode line 5 is electrically connectedto the APD array substrate 10 mounted in the mounting region α, and canbe used for application of a voltage to the APD array substrate 10. Theanode line 7 is connected to metal layers 65 and 66 to be describedlater, and is used in read-out of a signal transmitted from the APDarray substrate 10.

The APD array substrate 10 includes a plurality of APDs 20 which isarranged to operate in a Geiger mode. As illustrated in FIG. 4, theplurality of APDs 20 are two-dimensionally arranged in a photodetectionregion β of the semiconductor substrate 11 when viewed from thethickness direction of the APD array substrate 10. The photodetectionregion β has a rectangular shape, and overlaps the mounting region α ofthe circuit substrate 50 when viewed from the thickness direction of theAPD array substrate 10.

The APD array substrate 10 includes an N-type semiconductor substrate 11formed from compound semiconductor. The semiconductor substrate 11includes a substrate 12 formed from InP that forms the main surface 10A.A buffer layer 13 formed from InP, an absorption layer 14 formed fromInGaAsP, an electric field relaxing layer 15 formed from InGaAsP, amultiplication layer 16 formed from InP are formed on the substrate 12in this order from the main surface 10A side to the main surface 10Bside. The absorption layer 14 may be formed from InGaAs. Thesemiconductor substrate 11 may be formed from GaAs, InGaAs, AlGaAs,InAlGaAs, CdTe, HgCdTe, or the like.

As illustrated in FIG. 2 and FIG. 4, each of the APDs 20 is surroundedby an insulating portion 21 when viewed from the thickness direction ofthe APD array substrate 10. The APD 20 includes a P-type active area 22that is formed by doping the multiplication layer 16 with impuritiesfrom the main surface 10B side. Examples of the doping impuritiesinclude zinc (Zn). For example, the insulating portion 21 is provided byforming a polyimide film in a trench formed through wet etching or dryetching. The active area 22 formed in a circular shape when viewed fromthe thickness direction, and the insulating portion 21 is formed in anannular shape along an edge of the active area 22. The insulatingportion 21 reaches the substrate 12 from the main surface 10B side ofthe semiconductor substrate 11 in the thickness direction of the APDarray substrate 10

FIG. 5 is a view illustrating a part of an avalanche photodiode arraysubstrate capable of being used in photodetector device according to amodification example of this embodiment. As illustrated in FIG. 5, theactive area 22 may be formed in an approximately rectangular shape whenviewed from the thickness direction. Here, the approximately rectangularshape is a rectangular shape with rounded corners. According to this,concentration of an electric field to the corners of the active area 22is suppressed. In this case, the insulating portion 21 is formed in anannular shape along an edge of the active area 22 having anapproximately rectangular shape.

The APD array substrate 10 includes an insulating layer 23 and aplurality of electrode pads 24. The insulating layer 23 covers thesemiconductor substrate 11 on the main surface 10B side. Each of theelectrode pads 24 is formed on the semiconductor substrate 11 on themain surface 10B side for every APD 20, and is in contact with theactive area 22. The electrode pad 24 is exposed from the insulatinglayer 23, and is connected to the circuit substrate 50 through the bumpelectrode 25.

As illustrated in FIG. 2, the circuit substrate 50 is connected to theAPD array substrate 10 on the main surface 50A side through the bumpelectrode 25. The circuit substrate 50 includes a plurality of outputunit 30. As illustrated in FIG. 6, the plurality of output units 30 areconnected to each other in parallel, and forms one channel 40. Each ofthe plurality of output units 30 is connected in series to each of theAPDs 20 provided in the APD array substrate 10. The output unit 30includes a passive quenching element 31 and a capacitative element 32which are connected to each other in parallel. Any of the passivequenching element 31 and the capacitative element 32 is connected inseries to the APD 20.

FIG. 7 is a view illustrating a circuit configuration capable of beingused in a photodetector device according to a modification example ofthis embodiment. As illustrated in FIG. 7, a plurality of channels 40may be formed in the circuit substrate 50. In this case, each of thechannels 40 is formed by a plurality of output units 30 connected toeach other in parallel. At least one of the plurality of channels 40 maybe formed by the plurality of output units 30 connected to each other inparallel.

The circuit substrate 50 includes a silicon substrate 51, and a wiringlayer 61 stacked on the silicon substrate 51. As illustrated in FIG. 2,the silicon substrate 51 includes a P⁺ layer 52, a P⁻ layer 53, and a P⁺layer 54 in this order from the main surface 50B side to the mainsurface 50A side. The P⁺ layer 52 is provided by doping the P⁻ layer 53with impurities. The P⁺ layer 54 is provided by doping the P⁻ layer 53with impurities. Examples of the doping impurities in the P⁻ layer 53include boron. For example, an oxide film layer 60 formed in an elementisolation process by thermal oxidation is provided between the siliconsubstrate 51 and the wiring layer 61. The P⁺ layer 54 is exposed fromthe oxide film layer 60, and is in contact with the wiring layer 61.

The wiring layer 61 includes an insulating layer 62, a ground electrode63, an electrode pad 64, metal layers 65 and 66, vias 67, 68, 69, and70, polysilicon layers 71, 72, and 73, and a dielectric layer 74. Theground electrode 63, the electrode pad 64, the metal layers 65 and 66,the vias 67, 68, 69, and 70, the polysilicon layers 71, 72, and 73, andthe dielectric layer 74 are provided for every APD 20. The groundelectrode 63, the electrode pad 64, and the metal layers 65 and 66 areformed in the same layer. In other words, the ground electrode 63, theelectrode pad 64, and the metal layers 65 and 66 are formed at the sameheight in the thickness direction of the circuit substrate 50.

For example, the insulating layer 62 is formed from SiO₂. For example,the ground electrode 63, the electrode pad 64, and the metal layers 65and 66 are formed from Al, AlCu, AlSiCu, or the like. The groundelectrode 63, the electrode pad 64, and the metal layers 65 and 66 maybe formed from the same material. For example, the vias 67, 68, 69, and70 is formed from tungsten (W). For example, the dielectric layer 74 isformed from SiO₂ or Si₃N₄.

The wiring layer 61 is covered with the insulating layer 62. The P⁺layer 54 of the silicon substrate 51 is connected to the via 67 exposedfrom the insulating layer 62 of the wiring layer 61 to the siliconsubstrate 51 side. The P⁺ layer 54 is connected to the ground electrode63 through the via 67. The ground electrode 63 is disposed with respectto the electrode pad 64 and the metal layers 65 and 66 through theinsulating layer 62 at an arrangement height of the ground electrode 63in the thickness direction of the circuit substrate 50. The groundelectrode 63 is not directly connected to the electrode pad 64 and themetal layers 65 and 66.

The electrode pad 64 is exposed from the insulating layer 62 and isconnected to the APD 20 through the bump electrode 25. As illustrated inFIG. 8, a plurality of the electrode pads 64 are two-dimensionallyarranged on the main surface 50A side. Each of the electrode pads 64 isconnected to the polysilicon layer 71 through the via 68. Thepolysilicon layer 71 is connected to the metal layer 65 through the via69. The electrode pad 64 is disposed with respect to the metal layers 65and 66 through the insulating layer 62 at an arrangement height of theelectrode pad 64 in the thickness direction of the circuit substrate 50.The electrode pad 64 is not directly connected to the metal layers 65and 66. The polysilicon layer 71 is included in a first polysiliconlayer.

The polysilicon layer 71 constitutes the passive quenching element 31.According to the above-described configuration, the passive quenchingelement 31 is connected in series to the APD 20 through the bumpelectrode 25, the electrode pad 64, and the via 68. That is, a pulsesignal transmitted from the APD 20 is input to the passive quenchingelement 31 through the bump electrode 25, the electrode pad 64, and thevia 68. The pulse signal input to the passive quenching element 31 isoutput from the channel 40 through the passive quenching element 31, thevia 69 and the metal layer 65.

The electrode pad 64 is connected to the metal layer 66 at thearrangement height of the electrode pad 64 in the thickness direction ofthe circuit substrate 50. The metal layer 66 is connected to thepolysilicon layer 72 through the via 70. The polysilicon layer 72 isstacked on the dielectric layer 74. The dielectric layer 74 is stackedon the polysilicon layer 73. The polysilicon layer 73 is connected tothe metal layer 65 through a via (not illustrated). The polysiliconlayer 71 and the polysilicon layer 73 are formed at the same height inthe thickness direction of the circuit substrate 50. The polysiliconlayer 71 and the polysilicon layer 72 may be formed at the same heightin the thickness direction of the circuit substrate 50. The polysiliconlayer 72 is included in a third polysilicon layer. The polysilicon layer73 is included in a second polysilicon layer.

The polysilicon layer 72, the dielectric layer 74, and the polysiliconlayer 73 constitute the capacitative element 32. According to theabove-described configuration, the capacitative element 32 is connectedin series to the APD 20 through the bump electrode 25, the electrode pad64, and the via 68. That is, a pulse signal transmitted from the APD 20is input to the polysilicon layer 72 of the capacitative element 32through the bump electrode 25, the electrode pad 64 and the via 68. Apulse signal is output from the polysilicon layer 73 of the capacitativeelement 32 in correspondence with input of the pulse signal to thepolysilicon layer 72 of the capacitative element 32. The pulse signaloutput from the capacitative element 32 is output from the channel 40through a via (not illustrated) and the metal layer 65.

Both the passive quenching element 31 and the capacitative element 32are electrically connected to the electrode pad 64 and the metal layer65. Accordingly, the passive quenching element 31 and the capacitativeelement 32 are connected to each other in parallel.

Next, an operational effect of the photodetector device 1 will bedescribed with reference to FIG. 9 to FIG. 11. FIG. 9 illustrates apulse signal output from the APD 20. As illustrated in FIG. 9, a pulsesignal 26 from the APD 20 is classified into a fast pulse 27 and arecharge pulse 28. The fast pulse 27 is a pulse component having a peakvalue of the pulse signal. The recharge pulse 28 is a component that isdetected after detection of the fast pulse 27 and has a pulse widthlonger than that of the fast pulse 27.

FIG. 10 illustrates a waveform of a pulse signal output from the APD 20in a state in which the capacitative element 32 is excluded from theoutput unit 30 and a resistance value of the passive quenching element31 is set as a parameter. FIG. 10 is an integer graph in which a unit ofthe vertical axis is set as a current (A) and a unit of the horizontalaxis is set as time (s). Each of a plurality of pieces of data a, b, c,and d is data of the pulse signal in a case where a passive quenchingelement 31 having a different resistance value is provided in the outputunit 30. In the order of the plurality of pieces of data a, b, c, and d,the passive quenching element 31 having a higher resistance value isprovided.

As illustrated in FIG. 10, the smaller the resistance value of thepassive quenching element 31 is, the steeper an inclination of therecharge pulse 28 is. The steeper the inclination of the recharge pulse28, the shorter time necessary for quenching is, and the shorter deadtime for which light is not detected by the APD 20 is. When using thepassive quenching element 31 with a great resistance value, it ispossible to realize appropriate quenching in which occurrence of alatching current or the like is suppressed. However, the greater theresistance value is, the further the dead time increases.

A pulse width of the pulse signal from the APD 20 connected to thepassive quenching element 31 varies in response to the resistance valueof the passive quenching element 31. As illustrated in FIG. 10, thegreater the resistance value of the passive quenching element 31 is, thefurther the dead time of the APD 20 connected in series to the passivequenching element 31 increases. Accordingly, there is a demand for acircuit design including the passive quenching element 31 having anoptimal resistance value to make appropriate quenching and a reductionof the dead time compatible with each other and to secure photodetectionsensitivity and photodetection time resolution.

In the photodetector device 1, a plurality of the output units 30including the passive quenching element 31 and the capacitative element32 are provided in the circuit substrate 50 separate from the APD arraysubstrate 10. According to this, a space capable of forming theplurality of output units 30 can be further expanded in comparison to acase where the plurality of output units 30 are arranged in the APDarray substrate 10. Accordingly, the design of the plurality of outputunits 30 becomes easy.

Since the plurality of output units 30 are provided in the circuitsubstrate 50 separate from the APD array substrate 10, a parasiticcapacitance that occurs between the configuration of the APD 20 and theoutput units 30 can be reduced. A manufacturing process different fromthat of the APD array substrate 10 can also be used. Since manufacturingprocesses which are respectively appropriate for the APD array substrate10 and the circuit substrate 50 can be used, design of the plurality ofoutput units 30 becomes easy.

FIG. 11 illustrates a waveform of a pulse signal output from the APD 20in a state in which the passive quenching element 31 is set to aconstant value, and an electrostatic capacitance of the capacitativeelement 32 is set as a parameter. FIG. 11 is a univariate graph in whicha unit of the vertical axis is current (A) and a unit of the horizontalaxis is time (s). Data a is data of a pulse signal in a case where thecapacitative element 32 is excluded from the output unit 30. Each of aplurality of pieces of data b, c, and d is data of a pulse signal in acase where a capacitative element 32 having a different electrostaticcapacitance is provided in the output unit 30. In the order of theplurality of pieces of data b, c, and d, the capacitative element 32having a higher electrostatic capacitance is provided.

As illustrated in FIG. 11, when the capacitative element 32 is provided,a peak value of the fast pulse 27 is improved. The higher theelectrostatic capacitance of the capacitative element 32 is, the greaterthe peak value of the fast pulse 27 is. Accordingly, when providing thecapacitative element 32, time resolution of a pulse signal from theplurality of APDs 20 is improved. The greater the peak value of the fastpulse 27 is, the more easily the pulse signal from the plurality of APD20 is detected.

In the photodetector device 1, the capacitative element 32 that isconnected in series to at least one of the APDs 20, and is connected inparallel to the passive quenching element 31. According to theconfiguration, the peak value of the pulse signal from the APD 20 thatis connected in series to the capacitative element 32 can be improvedbased on the electrostatic capacitance of the capacitative element 32due to the characteristics described with reference to FIG. 11.Accordingly, the pulse signal from the plurality of APDs 20 is easilydetected, and the photodetection time resolution can be improved. Thephotodetector device 1 can count the number of incident photons whilerealizing desired photodetection sensitivity and photodetection timeresolution.

In a configuration in which the plurality of APDs 20 operate in theGeiger mode in the APD array substrate 10 formed from the compoundsemiconductor, electric field strength applied to the APDs 20 isreduced, and thus an influence of a noise can be suppressed.

The photodetector device 1 includes the polysilicon layers 71 and 73provided on the circuit substrate 50, the dielectric layer 74 providedon the polysilicon layer 73, and the polysilicon layer 72 provided onthe dielectric layer 74. The passive quenching element 31 is formed bythe polysilicon layer 71, and the capacitative element 32 is formed bythe polysilicon layer 73, the dielectric layer 74, and the polysiliconlayer 72. The polysilicon layer 71 is formed at the same height as inthe polysilicon layer 72 or the polysilicon layer 73 in the thicknessdirection of the circuit substrate 50. In this case, the plurality ofoutput units 30 can be formed in a simple manufacturing process.

Hereinbefore, description has been given of the embodiment of theinvention, but the invention is not limited to the above-describedembodiment, and various modifications can be made in a range notdeparting from the gist.

For example, the passive quenching element 31 may be formed by a metalthin film instead of the polysilicon layer 71. The capacitative element32 may be formed by two metal layers instead of the polysilicon layers72 and 73. In this case, the capacitative element 32 has a configurationin which two parallel metal layers sandwich the dielectric layer 74.

REFERENCE SIGNS LIST

1: photodetector device, 10: APD array substrate, 20: APD, 30: outputunit, 31: passive quenching element, 32: capacitative element, 40:channel, 50: circuit substrate, 71, 72, 73: polysilicon layer, 74:dielectric layer.

The invention claimed is:
 1. A photodetector device comprising: anavalanche photodiode array substrate in which a plurality of avalanchephotodiodes arranged to operate in a Geiger mode are two-dimensionallyarranged, the avalanche photodiode array substrate being formed fromcompound semiconductor; and a circuit substrate on which the avalanchephotodiode array substrate is mounted, wherein the circuit substrateincludes a plurality of output units connected to each other in parallelto form at least one channel, each of the output units includes apassive quenching element connected in series to at least one of theplurality of avalanche photodiodes, and a capacitative element connectedin series to at least one of the avalanche photodiodes and connected inparallel to the passive quenching element.
 2. The photodetector deviceaccording to claim 1, wherein the passive quenching element is formed bya first polysilicon layer provided in the circuit substrate, thecapacitative element is formed by a second polysilicon layer provided inthe circuit substrate, a dielectric layer stacked on the secondpolysilicon layer, and a third polysilicon layer stacked on thedielectric layer, and the first polysilicon layer is formed at the sameheight as in the second polysilicon layer or the third polysilicon layerin a thickness direction of the circuit substrate.